# Appendix E

Connecticut Department of Energy and Environmental Protection’s Review of the Seasonality of High PM 2.5 

## Days.

### E ‐ 1 

# Connecticut Department of Energy and Environmental Protection’s Review of the Seasonality of High PM 2.5 

# Days

This appendix explains the data sources, methodology and conclusions relating to an analysis of the seasonality of peak PM 2.5 

### concentrations. The purpose of this analysis was to determine if the highest
monitored PM 2.5 

### concentrations in Connecticut’s portion of the NY-NJ-CT PM 2.5 

### nonattainment area are limited to one season or can occur over two or more seasons during the year. If high PM 2.5 

### levels only occur in a single season, then invent ory development in support of PM 2.5 

### redesignation efforts should be focused on that season. If high PM 2.5 

### levels occur in multiple seasons, then an annual inventory can be used to support redesignation.

Methodology: Connecticut reviewed fully QA’d and certified PM 2.5 

### data from the 2004-2010 period, for the seven
southwestern Connecticut PM 2.5 

### sites (Bridgeport, Danbury, Norwalk, New Haven Criscuolo Park, New Haven State St, Westport and Waterbury). For each year, daily PM 2.5 

### concentrations were ranked for each site from highest to lowest concentration, with th e appropriate season identified for each day (i.e., Winter: Dec-Jan; Spring: Mar-May; Summer: Jun-Aug; Fa ll: Sep-Nov). Seasonal frequency during the 2004- 2010 period was then determined for two groupings of da ta: 1) The highest 2% of daily values each year (since the daily PM 2.5 

### NAAQS is based on the 98 th 

### %-ile value) and 2) The highest 10 days each year (to provide a more robust comparison). The highest 10 da y analysis was repeated for the most three recent years of data (2008-2010) to determine if recent large-scale regional reductions in sulfur dioxide emissions have influenced the seasonal distribution of high PM 2.5 

### levels (sulfate is typically the largest contributor to high summer PM 2.5 

### values, with less contribution during the winter 1 

### ).

Results and Conclusions:
Table 1 shows the seasonal distribution for the highest 2% of daily values 2 

### at each monitor for the period from 2004 through 2010. Overall, 49% of the highest PM 2.5 

### days occurred during the summer, with winter exhibiting a secondary peak at 35%, while 12% of the highest PM 2.5 

### days occurred during the fall season. There was minor variability between sites, with Danbury experiencing more high PM 2.5 

### days during the winter (43% of the total number of high PM 2.5 

### days) than the summer (38%) and Norwalk’s spring value (10%) at least double the value for the other six sites.

1 Bell, Michele et al. (2007) Spatial and Temporal Variation in PM2.5 Chemical Composition in the United States for Health Effects Studies. Environmental Health Perspectives. v15(7) p 989

‐ 995.

2 For sites with once

‐ in

‐ three

‐ day sampling, 2% generally represents the 3 highest daily values each year. For sites with every

‐ day sampling, 2% generally represents the 8 highest daily values each year.

### E ‐ 2 Table 1. Seasonal Distribution of the Highest 2% of Annual Daily PM 2.5 

### Concentrations (2004-2010)

Season Waterbury New Haven State St New Haven Criscuolo Westport Norwalk Danbury Bridgeport Overall Average
Summer 48% 48% 46% 57% 48% 38% 62% 49%

Fall 14% 14% 11% 5% 14% 14% 10% 12%
Winter 38% 38% 39% 33% 29% 43% 24% 35% Spring 0% 0% 4% 5% 10% 5% 5% 4%



### Table 2 summarizes the seasonal distribution based on th e annual highest 10 daily values at each site for the full 7 year period (2004-2010). Although the same general bimodal distribution (i.e., summer/winter peaks) is observed as was found for the top 2% of PM 2.5 

### levels, the results based on the highest 10 days each year reflect a greater occurrence of spring days than in Table 1 (12% versus 4%).

When the highest 10 day approach is narrowed to the most recent three-year period (2008-2010), as shown in Table 3, the overall bimodal results shif t such that winter becomes the predominant season (45% of the total number of high PM 2.5 

### days), with summer exhibiting th e secondary peak (36%). In the Northeast, the sulfate contribution to PM 2.5 

### levels is typically greater in the summer than in the winter season due to temperature and chemistry factors. Thus, a possible reason for the recently observed seasonal shift could be more stringent regional sulf ur emission limits imposed by the CAIR program on power plants.

Table 2. Seasonal Distribution of Annual Top 10 Daily PM 2.5 

### Concentrations (2004-2010)

Season Waterbury New Haven State St New Haven Criscuolo Westport Norwalk Danbury Bridgeport Overall Average
Summer 43% 46% 49% 43% 46% 43% 49% 45%

Fall 17% 14% 10% 10% 13% 13% 13% 13%
Winter 30% 29% 36% 36% 30% 31% 20% 30% Spring 10% 11% 6% 11% 11% 13% 19% 12%



### Table 3. Seasonal Distribution of Annual Top 10 Daily PM 2.5 

### Concentrations (2008-2010)

Season Waterbury New Haven State St New Haven Criscuolo Westport Norwalk Danbury Bridgeport Overall Average
Summer 37% 37% 23% 27% 43% 37% 50% 36%

Fall 10% 10% 10% 10% 10% 7% 7% 9%
Winter 43% 40% 60% 57% 37% 43% 33% 45% Spring 10% 13% 7% 7% 10% 13% 10% 10%



### Based on this analysis, high PM 2.5 

### levels occur throughout the year in Connecticut portion of the NY-NJCT area, with the highest frequency of events in the summer and winter seasons. Since high PM 2.5 

### levels occur in multiple seasons, annual invent ories should be used to support the PM 2.5 

### redesignation effort.